Page:Popular Science Monthly Volume 70.djvu/114

From Wikisource
Jump to: navigation, search
This page has been proofread, but needs to be validated.
110
THE POPULAR SCIENCE MONTHLY.

all the time required for the deepening and broadening of the main trough, the lateral stream was scarcely able to even scratch the lip of the hanging valley (Fig. 4). This point may be illustrated by a specific case, taken not from the Inside Passage, but from Nunatak Fiord, a branch of the Yakutat Bay Inlet which lies about midway between Sitka and Controller Bay just southeast of Mount St. Elias. This fiord has been so recently occupied by ice that vegetation, excepting scattered annual plants, has not yet been able to take hold on the soil. The Nunatak Glacier (Fig. II) has receded up this fiord more than a mile in ten years. Unquestionably there has been powerful glacial erosion here, for the walls of the fiord are smoothed and grooved by glacial grinding, and there are no valley spurs left. Several of the valleys tributary to the fiord are hanging high above it (Figs. 6

 

PSM V70 D114 View across disenchantment bay from russell valley.jpg

Fig. 10. Looking Across the Mouth of Disenchantment Bay, Russell Valley (Fig. 11) on Left. This valley is hanging at about sea level. A small valley to the right of this hangs fully 1.000 feet above sea level. A somewhat larger valley in the extreme right of the picture is hanging at a level intermediate between these two. To account for such discordance by faulting would demand very complex block faulting. But the rock walls of the fiord are plainly exposed and there is no evidence of it. Photograph by O. von Engeln.

 

and 7), and in all the larger of these small glaciers are still present. The entire absence of forest exposes the conditions here far more clearly than is the case along the forest-clothed Inside Passage.

Viewed from the fiord, the hanging valley selected for this illustration is plainly seen to be a broad, U-shaped trough heading well back in the mountains and with a small glacier at its head. The wide open mouth of this broad valley is truncated by the straight, steep rock wall of Nunatak Fiord and left perched high above even its water